This invention relates to a fan clutch and to its construction, and more particularly, to the use of such a clutch in vehicles or the like.
The present invention relates to an improvement of fan clutches and, in particular, to the improvement of efficiency of such fan clutches. Commonly used fan clutches in large trucks in the United States are constructed with a first clutch component being driven by a motor-driven pulley and having a frictional face, which is clutched to or separated from a second frictional clutch face on a driven clutch portion carrying fan blades. When the clutch faces are engaged they transmit full power without a slippage between the frictional faces. The clutch faces are typically engaged by a pneumatic or electromagnetic actuator with the pneumatic actuator requiring the use of air on the vehicle. U.S. patent application Ser. No. 60/095,498, filed Aug. 6, 1998 discloses a magnetic fan clutch where a magnetic field is used to join the driving portion to the fan blade driven portion.
The fan clutch used for large trucks or the like take considerable horsepower to accelerate and to overcome the inertia thereof and to provide the desired air flow to cool the radiator liquid being used or to cool a motor. For example, when the truck fan is of a 32xe2x80x3 diameter, the horsepower used to drive the fan can be as much as 40 to 80 hp for large trucks which have engines in the range of 200 to 600 hp. Typically, such large fans cause an air flow of about 2,000 cfm. If the amount of air flow can be increased so that a smaller diameter can be used, the resulting reduction in horsepower needed to cool the engine can result in increased fuel economy for the truck. The power used to drive a larger fan versus a smaller fan is not a linear increase but a much higher increase. Thus, any increase in fan throughput without an increase in fan diameter can be significant. Also, smaller fans can reduce the large amount of fan noise coming from a vehicle.
In Europe and in other places such as South America there is often used a viscous fluid fan clutch which is always rotating at speeds of 400 to 600 RPM, even when the fan is turned off. That is, the viscous fluid rotates the fan because of the friction and shears. When the viscous fan clutch is turned on, it never is able to produce or transfer 100% of the input power or torque because 7-10% of the power is lost with viscous fluid shearing. Because of the fluid viscosity and friction, this fan clutch is never totally disengaged to be free-wheeling as it is constantly engaged so that it is always using a considerable amount of the power. This power, of course, is wasted fuel consumption, which makes it a relatively inefficient fan clutch from a fuel economy standpoint. This particular fan clutch also uses a bi-metallic thermostat on the front of the fan assembly to measure temperature and a plunger is operated by the thermostatic switch, which requires ram air to operate. On slow moving construction vehicles or the like where there is relatively little ram air, such a thermo-statically controlled fan clutch is not readily usable. Likewise, for an ON/OFF fan clutch used on trucks there is a requirement for the use of compressed air which is often not available for construction or farm equipment and therefore makes the clutch less saleable to makers of such equipment.
Currently, it is desired to eliminate the 7-10% viscous shear inefficiency without an increase size of the radiators and to provide this increased efficiency to power the fan in order to run the engines hotter using the same cooling equipment. Thus, there is a need for increasing air efficiency to help cool these hotter engines.
With respect to each of these various kinds of fan clutches described above, there is a need for a new and improved fan clutch that has increased air moving efficiency.
In accordance with the present invention, a rotatable fan clutch having rotatable blades driven by a motor is provided with blades, vanes or fins to disperse air outwardly from a dead center of the fan at a central axis area to the location of the fan blades to increase the efficiency of the fan clutch. This is achieved by providing small interiorly-located vanes or fins that pump the air out of this central area to prevent a buildup of a bubble of air or negative pressure at the central area; and thereby provides an appreciable increase in the flow of air from the fan clutch.
In a preferred embodiment of the invention, the fan clutch-driven portion carrying the fan blades is provided with a central hub or cover with integral, curved fins or blades projecting from the central cover and shaped and sized to force air at the central area of the fan outwardly toward the fan blades, which continue to force the air to flow from the fan. That is, the air flowing toward the central axis of the fan is swept outwardly in a continuous flow by rotating curved fins or blades to join the continuous air flow being generated by the fan blades. In the preferred embodiment of the invention, the vanes are integrally molded with a cover and are curved between their inner and outer ends. By way of example, in the illustrated embodiment, the fan output was increased from about 2,100 cfm to 2,500 cfm with the addition of these rotating vanes causing air flow from the central area of the rotating fan clutch.
Inexpensive plastic vanes may be integrally molded on a separate plastic cover or cone which is fastened to the driven fan portion of the clutch. In the embodiment illustrated herein, the fan clutch is a magnetic fan clutch with a molded, plastic, driven clutch portion and a separate, discrete, molded plastic cover element, which has the vanes and which is fastened to the molded, plastic, driven portion of the magnetic clutch.